Hello again, I took my zj out yesterday and did a little off roading (everything went fine) then on the way home, on the freeway my zj had barley any power(hp) and had problems getting above 40-60 mph. Under hard accel my check engine light came on and was blinking (not on now) The rpms would shoot up but didn't seem to go anywhere, it does not feel like a transmission problem(I know what slipping feels like) Ive been doing a little research on this and have read a lot of different things, has anyone else had this problem? fixes please? I am very worried about this one, drove it today and still seems to have the same problem, could it be a clogged cat, misfire? bad 02 senor(s), bad air leak? Please help! 5.9zj has 152,000 and some change on it. Thanks in advance!

@ sevenscrew- the has rattled a little bit since i have had the zj. I am thinking the cat could be clogged?, but is there a real way to check without hacking it off? also if it was it surely would have encountered this problem sooner? @ oldfrog- No, no water what so ever, just did a oil change and filter at 152000 miles. Yes it does rev correctly in park, but still kinda sound like it has a vacuum leak, i was under there a little while ago but it was very hard to hear anything like a vacuum leak...

have not checked the trans oil yet. but im assuming it doesn't have water in it.

that could be the problem, it does not seem to sound "as beefy" as it did earlier in the day, does anyone know why i had a hard time getting about 60 mph tho? It seems like the power is not getting transferred to the wheels. It seems to be running perfect, idle is good, and i did not see anything out of the norm from under the hood.

Disconnect the neg battery terminal, unplug the downsteam o2 sensor, reconnect the battery, and see if runs better. Follow the same procedure for the upstream o2 sensor and if either one of these causes your ZJ to run better most often it's a bad sensor.

Also have you checked for codes? A clogged cat won't throw a code but it's worth checking codes to narrow your problem down. Good luck.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)

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I will try that in the morning. I have checked for codes with my obd-2 but it did not throw any. Also tried the on/off/on/off/on/off and did not throw any in the dash.The CEL was only blinking under hard accel then would go away and come back on under hard accel. Pretty stumped here.

When my cat was plugged, it ran about 5 degrees high at cruise. Under hard acceleration it would start bogging at about 2K at would not turn over 3K. As the power demand increased the temp would increase by about 10 more degrees and the valves rattled. If i stayed on it, it would misfire on #1 or #6 cylinder with a CEL . When I let up on it, the CEL went out.

Disconnecting the sensors as uni said is a good idea. It's easy enough and doesnt cost a thing except a trip or two under your jeep.

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